A liquefied natural gas facility typically converts feed gas into liquefied natural gas (LNG) and condensed natural gas liquids (NGL). A cascade liquefied natural gas facility typically includes multiple refrigeration units, which are used to progressively cool a natural gas feed to −161° C. Natural gas liquefies at this temperature with a 600:1 reduction in volume. This reduction in volume allows for economic shipping of the natural gas. As an example, a cascade liquefied natural gas facility could include a propane refrigeration system, an ethylene or ethane refrigeration system, and a methane refrigeration system. These refrigeration systems progressively cool the natural gas feed to produce liquefied natural gas, and the output of the ethylene or ethane refrigeration system can be processed to extract the natural gas liquids.
Control of a cascade liquefied natural gas facility is often difficult due to several factors. These factors include the large number of process variables that affect the operation of the facility, ever-changing ambient conditions, shifts in active process constraints, and changes in the composition of the feed gas. Under normal operating conditions, human operators typically make periodic adjustments to key operating variables of the facility. However, operators are often overwhelmed by the large number of process measurements being monitored, and they are often unable to keep up with the ever-changing operating conditions of the facility. As a result, the facility is often run at sub-optimal operation, resulting in a loss of production and a corresponding monetary loss.